A typical elevator system comprises an elevator car and a counterweight, each suspended on opposite ends of hoist ropes which are disposed in an elevator hoistway. The elevator system also includes at least two sets of guide rails extending the length of the elevator hoistway, with each set of guide rails being disposed on opposite sides of the hoistway. The guide rails guide a plurality of roller guides attached to the elevator car. Besides guiding the elevator car up and down the hoistway, the roller guides ensure a smooth ride of the elevator car by isolating the elevator car from excitation and leveling the elevator car within the hoistway.
There are several factors that impact the quality of the elevator car ride. One such factor is the total length of the hoistway. Longer hoistways require a greater number of guide rail segments stacked within the hoistway and a greater number of joints between the guide rail segments. A greater number of guide rail segments results in greater total weight of the guide rails and the resultant loading causes the rails to deflect. Also, the joints between the guide rails result in some discontinuity. Even slightly deflected rails and minimal discontinuity in joints cause the elevator car to vibrate and move laterally.
Another factor that adversely affects ride quality is an aerodynamic consideration. During vertical travel of an elevator car within the hoistway, aerodynamic car pulses created when the car passes the hoistway doors and/or counterweight cause lateral movement and vibration in the elevator car.
To minimize the adverse impact of rail imperfections and aerodynamics on the ride quality of the elevator car, a conventional roller guide assembly includes a suspension system and a damping system. The suspension system typically comprises a spring associated with each roller of the roller guide assembly to restore the roller to its original position after the roller has been deflected by imperfections in the guide rails. It is desirable to have a relatively soft suspension system to isolate the elevator car from rail imperfections.
Existing damping systems comprise a hydraulic cylinder to reduce vibration. However, the hydraulic damping system increases the stiffness of the suspension system. Increased stiffness of the suspension system is not desirable because of the resulting increase in guide rail excitations transmitted to the car, which in turn increases the vibrational response. Additionally, hydraulic damping systems require regular maintenance, sustain wear, and increase cost of the overall system.
Although the conventional roller guide assemblies are sufficient to ensure a relatively smooth ride for a typical elevator, high rise buildings and a continuous desire for improved ride quality demand improvements to the existing roller guide assemblies. Existing systems are not compatible with higher speed elevator cars riding on much longer stacks of guide rails because the higher speeds of the elevator car amplify aerodynamic factors and longer guide rail stacks increase loading impact. Therefore, a roller guide with a soft suspension system and an improved damping system are desired.